Ultrasonic Machining Process is a non-conventional machining process used for machining both conducting and non-conducting materials. This machining process can be used to machine such materials that cannot be machined by the conventional machining process. Ultrasonic Machining is mainly used in brittle materials.
As the name suggests, the machining process makes use of ultrasonic vibrations in the range of 20 to 30 kHz.
The ultrasonic wave is defined as an inaudible sound with high frequency for humans. The frequency of the ultrasonic wave generally exceeds 20 kHz.
These high-frequency vibrations combined with slurry is used in the ultrasonic machining process.
In this machining process, the abrasive slurry is used.
There are four types of abrasive slurry:-
1 Aluminium Oxide.
2 Silicon Carbide
3 Boron Carbide
4 Diamond Dust
These four types of slurry are used in ultrasonic machining based on the material which is to be machined.
Aluminum oxide is very light in nature and loses its sharpness very quickly. Diamond dust is the hardest among these four slurries and it is used for machining very brittle materials.
Silicon carbide and boron carbide have hardness in between the diamond dust and aluminum oxide. These two slurries can be used individually or a mixture of both these can be used as a slurry.
Ultrasonic Machining works on the basis of magnetostrictive action.
In magnetostrictive action, when we send frequency to the transducer, the transducer will change this frequency to vibration.
This transducer is a kind of electromagnet, when we provide it an electric signal then it converts it into mechanical vibrations.
It will work at more than 20,000 oscillations per second. It is a silent process as the human ear cannot hear this high frequency and so it is called ultrasonic frequency. Hence, the machining process is called ultrasonic machining.
The tool used in this process will be of soft metal so that we can easily give any shape to the tool easily. The cavity produced in the machining will be of the same shape as that of the tool. So the tool is chosen of soft metal so that it can be molded to any shape.
Parts of Ultrasonic Machining Process:
1 Power Supply:
This machining process requires an alternating current power supply generally of 50 to 60 Hz. So, a AC power supply is available to start the process.
2 High Frequency Generator:
High frequency generator is also called an ultrasonic power supply or electronic oscillator. It is used to convert conventional electrical supply typically 50 Hz or 60 Hz to high-frequency electrical energy. Frequencies of 20 to 40 kilohertz are the most commonly used. Then these frequencies are supplied to electro-mechanical transducers.
This transducer is of magnetostrictive type. After converting into a magnet, this transducer will change the frequency into mechanical vibrations by working on the basis of magnetostrictive action. This transducer will vibrate in up and down motion.
4 Utrasonic Amplitude Transformer Or Tool Horn:
It is also called a tool concentrator. The vibration amplitude generated from the transducer with the limit being approximately 0.025 millimeters is not adequate for machining. It is used to increase the vibration amplitude. It also guides and focuses the vibration towards the tool tip.
The tool is connected to the lower end of this tool horn which will help in removing materials. The tool is connected to the tool horn either by welding or screwing or brazing or soldering.
5 Tool Holder:
A tool Holder is used to grip the tool.
The tool used in ultrasonic machining is generally made of a strong tough and brittle material that does not fail under brittle fracture and ductile such as tungsten carbide, stainless steel, titanium, copper, etc.
The tool is used to remove materials from the workpiece.
Tools is manufactured in the same shape as the cavity needs to be created on the workpiece surface.
7 Cooling Mechanism:
On top of the transducer, a system is present for cooling purposes. Cold water is entered from an entrance and will receive the heat from the transducer and will escape through the exit. There is a casing around the transducer for cooling purposes and the water will flow inside this casing.
The slurry consisting of hard abrasive particles generally silicon carbide, boron carbide, and alumina mixed water or oil are provided constantly at the machining area.
The pump is used to supply abrasive slurry at the nozzle.
The nozzle is made up of tungsten material. Tungsten is used to make a nozzle because the slurry which comes from the pump can damage the nozzle if it is made from soft material, so it is made from hard material like tungsten.
- When an ac supply is provided to the high-frequency generator. It amplifies the frequency of the input supply up to 20 to 40 kHz.
- This high-frequency input supply is fed to the electromechanical transducer which converts this energy into an ultrasonic vibration thus making the tool to vibrate in the longitudinal direction.
- The horn is the intermediary between the transducer and the tool holder. The horn is used to amplify the amplitude of the vibration generated by the transducer and then guides and focuses these vibrations onto the tool.
- The tool holder grips the tool as it vibrates. As the tool vibrates, the abrasive slurry is fed with the help of a pump at a constant rate between the tool and the workpiece surface.
- Then the tool is pressed on the workpiece very lightly so that there is enough space for the slurry to flow between the tool and the workpiece.
- As the vibrating tool is pressed over the workpiece, thehigh kinetic energy of vibration is transmitted to these abrasive particles and these abrasive particles impinge on the workpiece surface and due to abrasion at the microscopic level, the material is removed from the workpiece.
- The shape generated in the workpiece due to the removal of materials will be the same as the shape of the tool.
Parameter affecting the metal removal rate (MRR):
1 MRR is inversely proportional to the cutting area of the tool.
2 Vibrations also affect the removal rate.
3 The type of abrasive, its size, and concentration affect the metal removal rate directly.
Applications of Ultrasonic Machining:
1 Drilling round holes of any shape.
2 Step drilling.
3 Grinding the brittle materials.
5 Slicing and Broaching hard materials.
6 Machining the glasses, ceramics.
8 Tapening and Coining
Advantages of Ultrasonic Machining:
1 This process is used for both circular and non-circular holes in very hard materials like carbide, ceramics, etc.
2 This machining process doesn’t require heating workpieces.
3 If a workpiece is sensitive to thermal fluctuations it can be safely machined because this machining process produces very little heat.
4 It is suitable for both conductive and non-conductive materials.
5 A semi-skilled operator can operate the machine.
6 High accuracy can be achieved. The final product is very well finished and structured results.
7 It is burr less and distortion less process.
Disadvantages of Ultrasonic Machining:
1 Low material cutting rate.
2 The process is limited to the machine’s surface of a small size.
3 Shorter tool life.
4 Unwanted large grain sizes can cause defects.
5 Power consumption is high.
6 This process can only be used to machine materials with hardness above 45 HRC.
7 It is difficult to drill deep holes, as slurry movement is restricted.